You will only enter the rental portion so if you only rent out 1/2 you only depreciate 1/2 of the cost basis.  

Remember to allocate some of the basis to land, which can not be depreciated.

@crazygerbil , having read and  concurred  with @Critter-3  and @ee-ea , would like to point out that you need to keep very good records.  This is because when you sell the property, you will see the whole thing and will need to allocate the gains between the two "parts" so that the gain is properly taxes as capital gain and ordinary gain ( recapture of depreciation).  It would be good idea to have a tax professional set up the accounts the first year and then you use TurboTax to keep track. IMHO

pk